Landfill sites, which keep leachate in stabilization ponds without an advanced treatment system, are often found in Southeast Asia. Leachate in such landfill sites probably seeps underground from the bottom of ponds and/or overflows the banks during storms, resulting in contamination of surrounding agricultural areas. In this study, crops, soils and irrigation waters were sampled in wet and dry seasons to determine heavy metal(loid)s (HMs) in agricultural fields around a landfill site in Thailand. The results showed 42%, 68%, 61%, 45% and 39% of vegetables had higher concentrations than the standards of Zn, Cd, Pb, Ni and As, respectively, although corresponding soils and irrigation waters were not contaminated. The level of Cd in vegetables was significantly higher in wet season (p < 0.01), while such a seasonal difference was not observed in vegetable soils and irrigation waters. In paddy fields, HMs concentrations in rice shoots, soils and irrigation waters did not change significantly from dry to wet seasons. The concentrations of Zn and Mn in vegetables and As in rice shoots significantly decreased with distance from the landfill site (p < 0.05). Such a distance-dependent decline and seasonal variation of HMs concentrations in crops revealed importance of the landfill as the source of contamination.
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